Re: [PROPOSAL] ARM/FDT: passing multiple binaries to a kernel

On Fri, 13 Sep 2013 12:22:13 +0100, Ian Campbell [off-list ref] wrote:

On Fri, 2013-09-13 at 11:13 +0100, Grant Likely wrote:

quoted

On Wed, Sep 4, 2013 at 5:41 PM, Rob Herring [off-list ref] wrote:

quoted

quoted

For u-boot Andre has proposed some syntactic sugar over the "fdt"
command to make boot.scr more trivial to use. We would of course need to
implement support for using it in the relevant distro tools (but they
tend to be very distro/machine specific already, e.g. Debian's
flash-kernel)

And being machine specific is a PITA. flash-kernel is certainly not
something we want to expand on. There is not much love for boot.scr
either. There is work to address what are not really machine
differences, but largely vendor u-boot differences:

http://www.mail-archive.com/u-boot-0aAXYlwwYIKGBzrmiIFOJg@public.gmane.org/msg119025.html

One option for u-boot which already supports syslinux style menu files
is to adopt the syslinux multiboot parsing support:

http://www.syslinux.org/wiki/index.php/Doc/mboot

Even building it into U-Boot is problematic because it leaves older
machines out in the cold. Leif's port of Grub to U-Boot is far more
interesting since the distro can now be in control of the code that
loads the images and jumps into the kernel/hypervisor.

AIUI this is not being developed any further?

Last I checked the patches have been posted for merging, but it is
stalled on the Grub maintainer. I believe he wanted to fix a bug on the
raspberry pi before merging. Leif would know more. LEG isn't actively
working on it anymore since UEFI is the priority, but I wouldn't call it
abandoned.

quoted

quoted

We need to back-up and consider what this looks like in the end for
all the pieces and get input from folks on grub, UEFI, and armv8. The
UEFI answer may be this is a grub problem. For armv8, this proposal
does match up well as the kernel boot interface for v8 is DT. Despite
some claims, ACPI will not completely replace DT because of this.

Yes, for UEFI it is absolutely an OS loader problem. UEFI provides an
API and runtime environment. Grub is in general moving towards a boot
menu system and a tool for loading images. Actual booting however
should be done by a separate OS loader application. For Linux, this
will be an in-kernel UEFI Stub.

I'm not sure I follow your distinction between loading the images and
"actual booting". If grub loads the images and Linux stub does the
actual booting how does this stub locate the images which grub loaded?

(Note: this isn't implemented yet, but is in progress) The DTB will need
to be passed via the UEFI system table. Initrd is passed by modifying
the dtb with linux,initrd-* properties in the device tree.

In the Xen case, I think the original proposal is conceptually sound.
I'll quibble about a couple of the details, but I'll address those with
a reply to the original proposal. It makes perfect sense to use the same
mechanism as the initrd properties to tell the kernel about additional
blobs.

Or are you saying the stub should load the initramfs itself? How does it
know where to find it? Having the kernel in one config file (grub's) and
the initramfs in another (the Linux UEFI stub's) seems likely to result
in things getting out of sync. Having Linux's stub parse the grub CFG is
even less likely to work well IMHO.

The stub has the ability to load both the dtb and initrd itself by
adding "dtb=" and "initrd=" arguments, but it is currently limited to
loading images from the same filesystem that the kernel was loaded from.
GRUB (or gummiboot/refind/etc) is potentially more flexible.

quoted

 For Xen I would recommend taking the
Linux EFI stub code and doing the same thing. There really isn't a
need for a multiboot spec when you can rely on a runtime execution
environment for setting things up exactly as you want them.

If this works for Linux on EFI then I see no reason it could work for
Xen on EFI (assuming my questions above are just a result of my
misunderstanding something)

But... Xen also wants to support non-server and therefore non-EFI
systems i.e. u-boot. We also want to support v7 where EFI is not a given
even for servers AIUI.

I was only responding to the UEFI question, but that aside, I don't see
a problem with adding properties to the DT for telling Xen where they
are.

Given that I think it is a given that Xen will have some sort of
protocol along these lines, for use in these environments even if it
does the EFI stub thing on EFI systems. The question is shall we make it
more general and useful to others or just go our own way? I'd prefer to
do the former.

Yes, make it general. GRUB and the EFI stub will use it.

g.